A different comment syntax question

[Rob Cameron]

Thanks to Chris Maden for setting me straight.  I have been reading
the XML specification without a detailed knowledge of SGML.  Although
you can do this to an extent, this seems to be one of the small
exceptions.  (The big exception of course is the issue of parameter-entity
references in the external document subset.  An area for further work.) 

Chris Maden <crism at oreilly.com> writes:
> 
> [Rob Cameron]
> > Although the XML specification makes clear that "--" is not allowed
> > in comments, there is another case that is less clear.  Can the body
> > of a comment end in a single hyphen, that is, is a comment like
> > "<--A+, A or A--->" legal?  There is no explicit mention of this in
> > the text of the specification, but a careful read of the grammar
> > does not allow it.
> 
> Correct.  The production reflects the SGML reality that -- ends a
> comment.  In SGML terms:
> 
> '<!'         starts the comment declaration in your example.
> '--'         starts the comment.
> 'A+, A or A' is the content of the comment.
> '--'         ends the comment.
> '-'          is an error.
> '>'          could be considered to end the comment declaration, but
>              we're now in error-recovery mode, and outside the scope
>              of the specification.
> 
> <!--A+, A or A- --> is a legal comment.
> 

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